When mowing grass on large acreages, such as golf courses, parks, large estates and commercial areas, it sometimes requires almost continuous mowing. Mower blades, under such conditions, continuously need to be sharpened. It is desirable that the blades be removed from the mowers for such sharpening and that consequently, a simplified means of detaching and attaching the mower blade to its drive shaft is desirable.
One of the factors that makes a simplified structure for such a purpose difficult to design is a safety factor. Since a blade rotates at a relatively high speed, it is necessary that the means of attaching the blade be completely reliable in order to prevent accidents or damage to property. Also, the nature of a lawn mower is such that stones and other foreign matter are often contacted by the mower blade which tends to scour or damage connecting elements holding the blade on the shaft. Often, such damage to the connecting elements will create a hardship in removing that blade for sharpening purposes.
There have been many attempts to install a quick attachable and detachable blade system on lawn mowers. Most of these rely upon removing and replacing only the outer cutting blade portion of the mower blades. One of the problems with such a system is that the blade attachments tend to break off at their connection. The high rate of rotation of the motor itself causes these blade portions to be thrown, and should they find their way out from under the mower housing, they can do considerable damage and injury to people and property.
Another method of providing a quick attachable and detachable mower blade assembly is by use of a unique arrangement of blade holder and blade developed and designed by Mr. James L. Rittenhouse and shown and described in his U.S. Pat. No. 4,586,257 which issued May 6, 1986. In this assembly, he provides a downwardly opening, U-shaped in cross-section blade holder. A blade is slidably received in the opening of the U-shaped holder. Upon the blade reaching a desired location with respect to the holder, an opening in the blade is positioned to receive a downwardly biased locking pin that holds the blade against further sliding action. Mr. Rittenhouse has provided notches in the leg portions of the U-shaped holder and notches in the opposite edges of the blade so that when properly aligned, the blade may be placed in the holder from beneath and then slid to its proper cutting position where the locking pin automatically inserts itself.
Some of the problems relating to Mr. Rittenhouse's design is that the notches in the edges of the blades and holder create stress areas that may cause premature failure of them. Should a stick, small stubble or other objects strike the pin and depress it momentarily while mowing, the blade could become unlocked and free to move radially, which could create a dangerous condition. Also, the only thing restricting the sliding movement of the blade relative to the holder is the single locking pin. Rupture of this pin would create a condition in which the blade was free to move or slide with respect to the holder. This could create a condition in which the mower blade could cause considerable damage to the mower deck or housing and could create a hazard to property and people working around the area of the mower.